The pyridazinone compounds to be used in the present invention are known in literatures, are known to have superior platelet aggregation inhibitory activity, heart stimulating activity, vasodilative activity, anti SRS-A (Slow Reacting Substances of Anaphylaxis) activity, thromboxane A.sub.2 synthase inhibitory activity and the like, and are expected to be useful as antiplatelet agents and the like (EP 482208, EP 744950).
The present inventors have now found with regard to compositions for oral administration, which contains pyridazinone compounds, that (a) pyridazinone compounds are relatively stable to heat, light, moisture and the like but show less dissolution after oral administration because their solubility in water starts falling at about pH 4 and they become hardly soluble at the neutral range, and (b) bioavailability (hereinafter to be abbreviated as BA) which shows absorption by dogs after fasting is low (about 10%) and the absorption shows great interindividual differences. They have concluded, therefore, that these problems in terms of dissolution and absorption of pyridazinone compounds need to be resolved before using the compounds for preparations for oral administration.